The use of a touch input device disposed over the viewing surface of a computer display to provide a "user friendly" means for the control of a data processing system is well known in the art. These devices are designed to allow an unsophisticated user to perform desired tasks on a computer system without extensive training. Human factor studies have shown that an input device which allows the user to input data directly on a computer display, generally known in the art as a touch input device, achieves the greatest immediacy and accuracy between a human and a machine. Most computer system software providing for user interaction is designed primarily for user input in the form of keystroke data. A growing body of software, especially that designed for desktop systems, accepts input from input devices which are typically actuated by touch to a tablet. These devices are particularly well suited for character input.
One such touch input device uses a frame which fits around the display screen having a number of infrared or visible light transmitters and receptors arranged in parallel horizontal and vertical directions. When the users finger blocks the light beams, the horizontal and vertical receptors note the absence of the signals, thereby locating the position of the action desired by the user.
Another class of known touch input devices use transparent overlays placed over the display screen. These touch overlays use a variety of means of detecting the presence and location of either a stylus or finger on or near the display surface.
Some such touch overlays use capacitive or resistive means in the transparent overlay and associated electronics, to detect the input of a user by finger touch. This type of input device can detect the location of a finger touch by the change in capacitance or impedance of the overlay. Yet other touch overlays use a stylus for user input, either to change the capacitance or impedance at the touched location on the touch screen or to return the electromagnetic or electrostatic signals generated by the overlay to a microprocessor to determine the stylus position. Digitizing apparatus is often used for achieving these functions.
It would be advantageous to the user, and simplify the apparatus, if any one of a multiplicity of overlays, each depicting or emulating a different but a familiar user touch pad interface or pattern, could be coded for specific use with any one of a myriad of programs and routines accessible to the programs